BMW uses many different connector types. In this post I'm going to go over the two types I've come to understand pretty well.
The first type uses 2.5mm circular male and female terminals. Some connectors that use these types of pins include but are not limited to the following: C101, C191, X20, X69, X6031, X33
In the image below you can see the male and female pins circled in red.
I also developed a de-pinning tool to help with any custom wiring or restoration jobs.
Some of these connectors can be a little tricky. In the image below see how the connector can become locked. This is the c101 connector. It is a two part assembly. There are two plastic concentric parts that rotate and index into different positions. Depinning should not require much force. Study your connector and make sure it doesn't have a locking mechanism.
Now moving on to the next connectors that are commonly used on these cars. These are the Bosch style connectors. Below are a 5-pin female and 2-pin male style.
Unfortunately, BMW decided to permanently lock the connectors which prevents them from being de-pinned. Let me show you what I mean.
Circled in red you can see where they heated up the connector and pressed down into the cavity where the wires are. This prevents the wire from being evacuated. Even if you have the correct de-pinning tool, the wire will get stuck and not back-out all they way.
Here you can see where that little nub is.
The best fix for this is to replace the connector entirely. The connectors I sell are not locked. I also sell a de-pin tool that will work on the connectors I sell.